1. Field of the Invention
This invention relates to terpolymers of maleic anhydride, a C1-C4 alkyl vinyl ether and isobutylene, and, more particularly, to a continuous, solvent-free process for making solvent-free, fine white powders of such terpolymers having advantageous properties useful for oral care compositions.
2. Description of the Prior Art
A batch, solvent-free process (i.e. no solvent other than reactants themselves) for making fine powders of high molecular alternating terpolymers of maleic anhydride (MAN), a C1-C4 alkyl vinyl ether (AVE) and isobutylene (IB) is described in U.S. Pat. Nos. 5,959,053 and 5,939,506. In such process, excess AVE and IB monomers are present over a 1:1 molar ratio of monomers, to function both as reactant and solvent in the system. No other solvent is present in the reactor. Accordingly, after stripping the excess AVE and IB from the reaction product, a solvent-free terpolymer is obtained. However, a batch process requires an extended amount of time to effect the reaction, usually necessitating about 9-13 hours to complete each batch.
Accordingly, it is an object of this invention to provide a continuous, solvent-free process for making solvent-free, fine white powders of terpolymers of MAN, AVE and IB having advantageous properties useful for oral care compositions.
What is described herein is a continuous, solvent-free process for obtaining solvent-free, fine white powders of high molecular weight alternating terpolymers of maleic anhydride (MAN), a C1-C4 alkyl vinyl ether (AVE) and isobutylene (IB), without odor or taste, having the molecular structure (A-B)n, where A is MAN, B is AVE or IB, and n is an integer indicative of the molecular weight of the terpolymer preferably containing 5 to 45 mole % of IB.
The process herein comprises feeding continuously alkyl vinyl ether and isobutylene as monomer reactants and solvent in excess of the desired 1:1 mole ratio of A:B in the copolymer, molten maleic anhydride and a free radical initiator, at predetermined feeding rates, into a reactor heated at a reaction temperature of about 50 to 100xc2x0 C., holding the reactants in the reactor for a predetermined average residence time, continuously withdrawing reaction product, residual alkyl vinyl ether and IB and initiator at the same rate as the feed rate of reactants into the reactor, stripping residual alkyl vinyl ether and isobutylene from the reaction product, drying the terpolymer obtained of any remaining traces of alkyl vinyl ether and isobutylene, and recycling recovered alkyl vinyl ether and isobutylene back into reactor.
In the preferred embodiments of the continuous solvent-free process of the invention, the alkyl vinyl ether is methyl vinyl ether, the mole ratio of a total of IB and methyl vinyl ether to molten maleic anhydride is about 25:1 to 5:1, most preferably 12:1 to 7:1, the initiator concentration is 0.01 to 0.2% based on the weight of copolymer, and the % copolymer solids removed from the polymerization reactor is about 10 to 40%.